PIC RPTS ACFT HAD BEEN ON DSCNT AND ATC SUDDENLY ASKED TO INCREASE RATE OF DSCNT. AFTER COMPLYING; ANOTHER CTLR CAME ON AND ANGRILY GIVES RADAR VECTORS TO AVOID A LOSS OF SEPARATION FROM ACFT Y. NO SYS ERROR; BUT CLOSE.

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ON A RETURN TRIP TO MDT FROM CYYZ WE WERE GIVEN A STEADY AND EARLY DSCNT FROM A LONG WAY OUT. WE BEGAN DSNDING AT ABOUT 1000-1200 FPM AND HAD BEEN IN THAT STATE FOR ABOUT 50 MI. THE ORIGINAL CTLR CALLED US BACK AND ASKED US TO 'EXPEDITE OUR DSCNT.' WE COMPLIED AND MOVED TO ABOUT 2500 FPM DSCNT RATE. ANOTHER CTLR CAME ON IN A FEW SECONDS AND RATHER ANGRILY TOLD US THAT WE WERE 'TOLD TO EXPEDITE DSCNT.' AT ABOUT THAT TIME WE GOT A TCASII ALERT OF 'TFC.' THE CTLR SIMULTANEOUSLY TOLD US TO TURN TO A NEW HDG OF 90 DEGS OFF OUR FLT PATH. AFTER CLRING THE ALERT (SOME DISTANCE AWAY) WE DISCUSSED THE POSSIBILITIES THAT HAD LED TO THIS EVENT. WE DETERMINED THAT THE ORIGINAL CTLR MIGHT HAVE BEEN IN TRAINING AND GOTTEN SOMEWHAT BEHIND THE UNFOLDING EVENTS. IF THE SECOND CTLR WAS A TRAINER WE DON'T BELIEVE THAT HE WAS WATCHING ALL THAT CLOSELY. A MORE TIMELY CALL TO EXPEDITE AT THE OUTSET MIGHT HAVE BEEN IN ORDER AS WELL. WE BELIEVE THAT WE COULD HAVE CHKED THEIR NEEDS AT THE OUTSET AND PROBABLY AVERTED ANY STRESS ON ANYONE'S PART. IF; INDEED; THERE WAS TRAINING GOING ON; PERHAPS A LESS BUSY SECTOR OR TIME WOULD BE MORE APPROPRIATE.